tests: verify that Python scripts are blackened

Scripts are Python too. They should be blackened.

(As suggested by Pierre-Yves in D7420.)

Differential Revision: https://phab.mercurial-scm.org/D7447

tests/test-check-format.t

@@ -1,5 +1,5 b''
 #require black
 
   $ cd $RUNTESTDIR/..
-  $ black --config=black.toml --check --diff `hg files 'set:**.py - mercurial/thirdparty/** - "contrib/python-zstandard/**"'`
+  $ black --config=black.toml --check --diff `hg files 'set:(**.py + grep("^#!.*python")) - mercurial/thirdparty/** - "contrib/python-zstandard/**"'`
 

tests/test-check-shbang.t

@@ -11,6 +11,7 b' look for python scripts that do not use '
 In tests, enforce $PYTHON and *not* /usr/bin/env python or similar:
   $ testrepohg files 'set:grep(r"#!.*?python") and **/*.t' \
   > -X tests/test-check-execute.t \
+  > -X tests/test-check-format.t \
   > -X tests/test-check-module-imports.t \
   > -X tests/test-check-pyflakes.t \
   > -X tests/test-check-shbang.t